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Why did Cessna get rid of manual flaps in their 172?
At the club I fly at, there is an older Cessna 172 that has a manual "Johnson Bar" that is used to put the flaps down.
In the newer 152, and I believe the rest of the planes (I have yet to fly them), the flaps are controlled via a electronic (or hydraulic?) lever.
It appears to me that the manual flaps are more reliable, more maintainable, and a hell of a lot more fun in my opinion. Additionally, the manually flaps don't require a lot of strength to operate IMO. Does anyone know why the automatic design is favored over the manual counterpart? Same question applies to car transmissions...

mechanical needs control rods/cables running through the frame

This guide has some interesting details.

Not electronic.  Electric.  It is just a switch and an electric motor (maybe some limit switches, too).  Electronics include electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies.

I did fly with a woman once who could not get the flaps down to 40 degrees. I guess it was a combination of seat in forward position and the bar way back and also it gets a bit heavy at the end. As I remember the bar was about her shoulder and you don't have much strength so far back. That is how I remember it anyway, it happened in the early '70's.

I think whether one prefers manual flaps or electrical is very much a matter of personal preference. Personally, I was very happy to move from manual flaps to electrical. And I'm unhappy to have to put up with Johnson bar flaps in the Cessna Skycatcher I'm checking out in. The bar is really in the way for me. I have to rest my forearm on the raised bar, and that's very uncomfortable.

Today, things like manual flaps with a giant bar on the floor are fun and interesting retro designs. Back in the 1960s powered anything was modern and progressive. The manual bar would have been as exciting as manual steering / transmission on your 1965 Buick Riviera. You can't promote a retro feature from the originating era.

Re: car transmissions... manuals were developed before automatics were figured out. Automatics exist because they require less driver skill to operate, making cars more accessible to more drivers. Manuals persist because they are more fun to drive and can be more fuel efficient.

I loved the Johnson bar in the Piper

Re: 2nd reason for automatic car transmissions... As an American who has spent his entire life driving manual transmissions and then takes a trip to the UK and rents a car, realizing only at the last moment that the shift lever will be on his left, which he has never done in his life, I was grateful for a rental company that could find an automatic for me. I'm sure I could have driven it, but it would have been awkward at first and taken some getting used to. I didn't need that added distraction when driving on the "wrong" side of the road.

Nobody can definitively answer this for you except Cessna's 1965/1966 engineering team (the year they made the change), but there are two reasons I can think of:
Because switches are cooler than Johnson bars; or Because everyone else is doing electric flaps.
Much like with manual transmissions, some people just don't like the extra work of manual flaps, and for those folks electric "flip a switch and don't worry about it" flaps are a selling point.

In terms of reliability it's a trade-off (as are all engineering decisions), so let's look at a few of the factors:
Mechanical Flaps

+Flaps still work when the battery is dead.
+The pilot can control the extension/retraction rate to some extent.
+Usually cross-linked with a bar (so you can't have a "split-flap" condition)
+Simple to rig, adjust, and maintain.
-Actuation requires more pilot skill
You need to develop the muscle memory to grab the handle without looking.
You need to learn to govern the extension/retraction rate smoothly.
-The failure mode is usually "Flaps Up"
You could lose your flaps on short final if the cable or lock mechanism fails.

Electric Flaps

+"Easier to Operate" (you don't need to reach down to the floor)
+Extension/Retraction rate is constant (governed by the motor)
+Fewer moving cables running through the fuselage (wires replace them)
+Typical failure mode (e.g. dead battery) is "Flaps stuck where you left them"
Less chance of losing your flaps on short final.
+Depending on the design they may save some weight over a mechanical system.
-You lose control of the flaps if the battery dies (no-flap landings are more likely)
-You have one or more motors to maintain/replace if they fail
-Depending on the design it's possible to have a "split-flap" condition

Cessna's engineers and marketing folks looked at those factors (and probably many others) and decided that electric flaps "made sense". On the other side of the GA fleet, Piper's engineers looked at the same factors and decided to keep the Johnson bar flaps (which are still found in the PA-28 series today).
From a manufacturing standpoint it makes sense for all of the aircraft a manufacturer produces to use the samecontrol mechanisms -- either all the planes use mechanical flaps or all the planes use electric flaps because it simplifies production and allows everything to run through on one assembly line rather than stopping at the flaps and diverting aircraft to different teams.

I guess I'm just bitter that they didn't go with "let's make it an additional feature"

The older I get, the less I like gimmicky things like electric flaps and the more I like good simple mechanical linkages.  Failure rates are comparable, but diagnostics and repairs are so much easier on mechanical...

Just a side note, Johnson bar systems can encounter the split flap issue and it happened to one of the Warriors I fly in (not while I was in it though)

@Dave Yeah, in the PA-28 you can have a pushrod (or more likely cotter pin) failure that has the potential to really ruin your day (one flap is no longer linked to the torque tube). Likewise the cause of split-flap conditions  in light GA planes' electric flap systems seems to be flap rollers coming off the track (as opposed to any intrinsic problem with the electric aspect of the system) - You could have an electric system that moves a torque tube and be in the same situation as Johnson-bar/pushrod flaps as far as split-flap conditions go.

Electric flaps in the Cessna Cardinal drive fowler flaps, which move down and back when they deploy. I suggest having that kind of movement would be difficult to do with a bar.  Electric motors and limit switches, even tho flap type is different than other Cessnas like 150/152, 172, maybe even 182.

There are some great answers here, but as someone who spent some time flying a C172C with manual flaps, I prefer electric flaps. Probably the most notable improvement with electric flaps comes in performing a go-around. Imagine you're on short final, in-close and slow with 40 degrees of flaps and you need to go around. Ok so full throttle, you get a healthy serving of torque, along with a nose that wants to aim at the sky, push that right rudder while pushing the nose level and at the same time pull up that flap handle and push the button to release the lock and then lower it trying to find the 20 degrees setting. While you're doing that you're wishing your right hand was free to start trimming down that nose. Its easy to incrementally add flaps, but incrementally decreasing the flaps was tough for me because you can't just pull up until it clicks... the locking system isn't designed to operate like that when lowering the handle.

Electric flaps were installed in the 1965 Cessna 172 because the Air Force specified electric flaps and offered to buy a lot of aircraft if the change was made.  As a result, the Air Force and Army bought a slew of them as the T-41 Mescalero (Credit to Wikipedia):

In 1964, the US Air Force (USAF) decided to use the off-the-shelf Cessna 172F as a lead-in aircraft for student pilots. The USAF ordered 237 T-41As from Cessna. The first USAF class (67-A) of students began training on the T-41 from the civilian airport in Big Spring, Texas, in August 1965.
The T-41B was the US Army version, with a 210 hp Continental IO-360 engine and constant-speed propeller in place of the 145 hp (108 kW) Continental O-300 and 7654 fixed-pitch propeller used in the 172 and the T-41A.
In 1968, the USAF acquired 52 of the more powerful T-41Cs, which used 210 hp (160 kW) Continental IO-360 and a fixed-pitch climb propeller, for use at the Air Force Academy in Colorado Springs. Four of these aircraft remain in service supporting USAFA programs.
In 1996, the aircraft were further upgraded to the T-41D, which included an upgrade in avionics[1] and to a constant-speed propeller.

This aircraft later became the Hawk XP and was sold for civil use - great airplane, I own one.  At a flight review 4 years ago, the very impressed newly minted flight instructor commented, this thing is a beast!

One can imagine a relatively simple and robust linkage between the lever and flaps on a low wing e.g. Piper Cherokee. Maybe not so straightforward for a high wing like a C-172, where there is likely already a complex cable routing for the ailerons.

Simple, yes. Robust.... well as robust as any other cable linkage in the control system I suppose :) (Getting the Johnson bar to work in a high-wing is just a matter of some different pulleys to change the angle - a little more complex, but no more than say the ailerons.)

I don't claim to know with any certainty, but pretty sure I once saw a cutaway illustration of the Piper (low wing) system showing pushrods, levers, and a torque tube - no cables.


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Is the Valsalva Maneuver safe?
The Valsalva Maneuver is where a pilot or passenger pinches their nose, closes their mouth, and then attempts to exhale through their nose. It is used to equalize or clear a buildup of pressure in the ear.  I'm always nervous when I do the maneuver, though. I'm afraid I'm going to damage my eardrums in some way.
Can performing the Valsalva Maneuver do damage to the ears, or is it entirely safe?

I've always meant to as a doctor how common it is to have voluntary control over the eustachian tubes. Somehow I learned that trick as a kid... I have no idea how to teach it to anyone else, though.

@keshlam I learned it by isolating the muscle movements that caused my ears to pop while swallowing.

@ratchetfreak: Something like that. Much the way I learned to twitch my ears by noticing that something caused my glasses to move.

@keshlam My instructor had at one time asked me why I didn't need to do this.  I told him I could do it without much effort.  I was kind of confused that he couldn't do the same, now I think I know why.  To teach it:  swallow while noticing the low-volume vibrating in your ears and the feel of the muscles around the ears.  Now try to make the same muscles move without swallowing.  If you are doing it right you will hear the same noise and muscles moving. I don't remember trying this when diving, but it works great at altitude.

Yes, it's safe. It's taught to scuba divers as a standard method for equalizing air pressure, with the general caveat that it should never take too much effort and if you feel any pain or discomfort from doing it then you should stop diving and consult a doctor. Since pressure changes in the air are much more gradual than those underwater, it shouldn't be difficult at all to equalize in an aircraft.

ditto. And after an altitude chamber ride one is advised to valsalva frequently for the rest of the day to prevent nitrogen build up. Nonetheless I woke up the next morning and my ears hurt like hell. It hurt to valsalva but the pain stopped immediately.

@radarbob I can't see any connection between the valsalva and dumping nitrogen (which is only ever a factor of time).

It is safe.  Start slow if its new to you.  I used it for years at the airlines with no issues.

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What is the status of a bravo airspace when the associated TRACON is evacuated?
On 18 March 2020, an earthquake struck just south of KSLC, causing an evacuation of the control tower and TRACON facilities.  The airport was closed.  Later in the day, I found myself unable to contact approach control.  The control tower at KPVU informed me that the TRACON was still closed, making radar services unavailable.
What I want to know is, does the bravo airspace stop existing when this occurs?  There was nobody to give me a clearance into the airspace.  Could I enter anyway, or should the airspace essentially be sterile?

If in doubt, stay out

In cases where a given unit of airspace (for example, a Class D circle around an airport with a tower) is only in effect part time, there is always a note to this effect in the FAA's "Airspace Designations and Reporting Points" document.  The current (August 2019) edition of this document is FAA Order JO 7400.11D.  The Class B airspace for KSLC is listed on pages B-25-26 and there is no notation that it is only in effect part-time.  In fact this is true of all Class B airspace.  Some Class C airspace is only in effect part time-- an example is Lincoln Airport (KLNK) in Nebraska.  However in such a case the airspace opens and closes according to a set schedule that is published in the Airport Facility Directory or in NOTAMs.
The Class B airspace at KSLC definitely does not stop existing when an unexpected circumstance closes the associated air traffic control facility.  In the absence of authoritative information to the contrary, you need to assume that you should not enter the airspace without a clearance.  Checking for NOTAMS would be one way to check whether the FAA has temporarily authorized some unusual procedure for the special circumstance you describe.
In a NOTAM search via this link selecting an "archive" search (click on "location" tab for this option) and using "KSLC" as the search term, we see various NOTAMs for March 18 (ILS approaches unavailable, etc) but nothing indicating that any part of the Class B airspace was temporarily revoked.  Some of the NOTAMS key to messages that may be seen on this
Air Traffic Control System Command Center website.  It appears that none of the NOTAMs or messages pertain to alternative ways to get clearance to enter the Class B airspace.

It's hard to believe that there was really no way to get into the KSLC Class B airspace for many hours.  Maybe someone else can find something in the NOTAMs or messages that I have missed.

Future edit-- " It appears that none of the NOTAMs or messages pertain to alternative ways FOR AN APPROACHING AIRCRAFT to get clearance to enter the Class B airspace."  Some of this messages do appear to pertain to alternative frequencies to use on the ground at KSLC.

Future edit-- "opens and closes" was really not the right phrase in first paragraph.  Meant something more like comes into effect and goes out of effect.

There may have been some procedure for getting clearance into the KSLC Class B airspace which the author of the question was not aware of it, but which didn't require a special NOTAM.  E.g. someone to ask other than TRACON.

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Why does this F18 have the rudders pointing towards each other?
I have seen this when they are parked and when taking off from the carriers.

Because ground effect was not considered during development.

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text:
Is there a button that pilots push to transmit on the radio?
Is there any button which needs to be pressed when the pilot or co-pilot wishes to talk to ATC?
Normally in videos on YouTube they don't seem to be doing anything special other than speaking, but I believe that there's more to it. Probably the push buttons (like on a walkie-talkie) are located very close to their hands?
I'm generally asking about all aircraft that communicate with ATC, not any specific airliner.
Please note that I know the handshake stuff and the frequencies and the radio part of it. My question is only about whether they do or they don't have a push button when they have to send a message. It doesn't seem to be an always on thing because obviously that would clutter up the channel and ATC guys don't need to listen to what the pilots are talking in the cockpit routinely.

There is usually a PTT (push to transmit) switch on the yoke or column, right under the pilots thumb.  Press and talk, release to listen.  You won't see it on a video.  Imagine pressing a button on the steering wheel of your car right under your thumb.

Thanks Simon, that makes sense. When the aircraft is flying on auto pilot and hands aren't necessarily on the Yoke do they still need to hold the yoke fist and press the button or there are alternate buttons too?

There is usually also a button on the control unit which does all of the audio switching and volume, often on the pedestal or console.

There is a push to talk (PTT) button located at the yoke or sidestick, in small and large aircraft likewise. When the PTT button is not triggered, all communication is routed through the intercom and not broadcasted on the frequency. Once the button is triggered, communication is broadcasted on the active frequency.
In the below picture of a glider, it is located on top of the middle stick.
On the second picture is it behind the yoke, to be used with the index finger.

(Image Source: WikiPedia)

(Image Source: Private Blog)

Really? I thought VOX will be used.

@Narayanan So far, I am not aware of any aircraft using this. I also doubt that in environments with high ambient noise this would be effective. It also would trigger when pilots talks to their copilots etc... so how to determine when it will be broadcasted on the frequency? PTT is still the technology of choice here.

@Narayanan: Pilots say a lot of things that are not intended for broadcast. So they must indicate that they want to say something that is.

Why is there a PDA mounted to the instrument panel?

@Someone Some pilots rather use a personal device for flightplanning or flightracking. Glider Pilots use handheld devices often. I personally use SkyDemon on an iPhone for Navigation in tight cockpits where I cannot mount my iPad directly anywhere.

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How do pilots/controllers deal with overlapping transmissions on the radio?
A disadvantage of the analogue radio1 used for communication is that it does not receive when it transmits. Everybody is trained to wait until the frequency is quiet before starting to talk, but it's still possible that two stations will start talking at the same time, in which case everybody else will hear an unintelligible mess but the two talking will not be aware of it. The station who talks longer won't be aware at all and if they talk for similar time, neither may be aware.
What I would like to know is how humans deal with the problem and whether there is any specific guideline for resolving these conflicts.
It seems like if the controller just says "calling centre, say again" the two may just both start talking past each other again.

1 Just like any other shared frequency radio, but digital systems seem to have more options to handle it, especially for the relatively low bandwidth requirement of voice communication.

in networking this situation is called carrier sense multiple access and the (unofficial protocol used would be aloha)

Lol, I just posted my answer which linked to the same thing -- I promise I didn't copy your link!  :)

@ratchetfreak, I know it quite well in networking and I know it can create serious problems for the simpler implementation. Tha't why I am wondering how humans rather than computers deal with it.

The normal way this is handled is that immediately after the conflicted transmission ends someone jumps on freq and transmits "blocked!".

@casey: That's basically what I wanted to know. Do you know whether it is mentioned anywhere (some regulation, AIM or such) or just a common practice people pick up after some time?

Usually when that happens you hear both of them overlapping, and the offenders would almost always notice as it seems like everyone on frequency can't wait to scream "BLOCKED!" right after their transmission

@JustinKiang which will be blocked as well continuing the loop ...

@JanHudec "Blocked" is actually standard phraseology - other than that the AIM has a few words on radio technique but nothing specific about what to do if your transmission was blocked - it's largely an area where common sense and courtesy seems to suffice :-)

Well in regard to "How are these situations resolved?" you've already answered your own question in a way: the intended recipient responds with something like "Blocked" or "Calling center, say again." (If they are expecting to hear from a specific aircraft they'll often respond with "N12345, say again.", and if the frequency congestion is really bad controllers may add "All other aircraft standby").
As kevin42 pointed out this is very similar to what digital CSMA/CD systems do - they detect a collision ("Blocked"), wait a while, and try their transmission again.

As a practical matter, two-way voice communication over the radio is possible, but difficult: for example a discrete "uplink" and "downlink" frequency as you have with some radio systems would be impractical in the sort of mesh topology that you have with aviation radio (you could implement it for a single air-to-ground pair trivially, but aviation radios are also used for air-to-air communication, and it's important that pilots hear what's going on as this enables them to build a mental picture of the airspace, as well as ensure that they're not blocking other pilot's transmissions).
Regarding analog-vs-digital, the traditional AM radio used in aircraft has one major advantage over its digital counterparts: when two digital signals overlap the result is garbage -- you can't recover any of the information. When two analog AM signals overlap you get heterodyning (the two signals mix, and your receiver pipes that mix into your ears).
The resulting mixed signal sounds AWFUL, there's an ear-bleeding squeal from the out-of-phase carriers and the voice modulations combine to a garbled mess much of the time, but with experience you can usually pick out one of the communications (particularly if you're close to one of the transmitters, where it will overpower the more distant signal).
The ability to step on a transmission as described above this can be useful: Instructions have been issued over a "stuck mic" before to get other aircraft off the frequency.
In a similar vein, if you have an emergency you probably aren't going to listen before you talk - you're going to key the mic with your mayday and even if the controller misses half of what you're saying under the heterodyne noise they'll know there's an emergency when they hear the other half of your transmission and tell everyone else to standby while they talk to you.
In both of those situations a digital system implementing CSMA/CD would detect that the frequency was in use and not transmit (and if were a digital system and transmitted anyway both digital signals would be garbled and unusable).

A digital system would need higher bandwidth to have enough time for the retransmits or some form of managed access. It would also be more expensive and less reliable and there is a big advantage to simplicity here. I was mainly interested about what aviators do when transmissions overlap, not really thinking that anything should be fixed (multiple people talking on a conference call does not cause any squeal, but is not any more intelligible anyway).

@JanHudec Honestly I think the big failing (more than the heterodyning from overlapping transmissions) is what you pointed out in your question: you can't hear the frequency when you're talking (which could at least theoretically be solved with some changes to the radio design 2 antennas - one RX and one TX. Not sure why nobody's built an aviation radio like that, except possibly our hatred for draggy antenna poles :)

Two antennas don't really solve anything. The transmitter would still feed a lot of energy to the receiver making it impossible to pick out and amplify the much weaker other signal. I asked about details over here. Unlikely to get it working on an airplane, but it could be doable on the ground, so at least the controller would know when their instructions are being blocked.

the second to last paragraph is why you repeat mayday a few times

Most of the time there will be an identifiable fragment of one transmission that will allow the controller to say, "Aircraft at flight level three three zero say again." After that interchange is completed, it is followed by, "Other aircraft calling Aloha center say again."

It isn't really an analog vs. digital problem. Even WiFi connections have the same problem, and they rely on built in collision avoidance techniques to make it work. But it turns out that what humans do is pretty similar to the collision avoidance techniques used in wireless communications.
For example, two people try to contact the tower at the same time and step on each other's transmission. So the tower doesn't respond to either. Both people try again after some amount of time. As long as there is just a tiny amount of difference in the amount of time they wait, one of the retransmissions will come first, and the other person will wait.
In uncontrolled airspace, when using the advisory frequency things aren't as simple, but in practice at least one of the people will stop talking first and realize they were colliding with the other and repeat their transmission. The bottom line is that I don't think this is a problem, except when the airspace is very busy, and in that case a different technology is unlikely to make much of a difference.


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How are condensation cones created by supersonic airplanes?
There are many awesome pictures of this phenomenon such as this one:

What is the physical explanation of how this occurs? Does it occur only when the airplane crosses the sound barrier or does it continue throughout the whole supersonic regime if enough water vapour is present in the atmosphere? What factors does this condensation depend on?

The Wikipedia vapour cone article isn't the most detailed but is a good place to start.

It is important to note that the vehicle is not traveling at supersonic speed when condensation collars (rockets) or condensation cones (aircraft) occur. It is merely close to the speed of sound.
From the vehicle's viewpoint
Air is accelerated by the displacement effect of the vehicle - it pushes the air aside and around itself, causing the flow to accelerate and to become supersonic relative to the vehicle. This acceleration is directly connected with lower pressure (see this answer for a detailed explanation), and air with high relative humidity will be pushed beyond its dew point, causing the water vapor to condensate. Please note that the onset of condensation is slightly delayed, so the fog is not strictly indicating the region of lowest pressure. Also, the forward cone is not the same as the forward shock front of a lambda shock.
However, the rear boundary of the condensation is indeed caused by a shockwave. The low pressure area is instantly ended by a compression shock, when the supersonic flow around the aircraft is abruptly decelerated to subsonic speed by a compression shock. This raises the local air pressure back to around ambient pressure, so the capacity to absorb water is raised again and the fog evaporates. Again, this happens with a slight delay, so the end of the condensation area does not coincide with the compression shock but follows it.
From the viewpoint of the air
Since the low pressure area is caused by the aircraft, it travels with the aircraft, and so does the condensation effect. The air around the aircraft or rocket is accelerated towards the vehicle by its pressure field, which causes the condensation. Now the air is so fast relative to the vehicle that it is decelerated and recompressed by a straight shock, causing the condensation to disappear again.
Factors
A relatively blunt vehicle traveling at close to Mach 1 and humid, almost saturated air are the factors which help this effect to occur. Note that you can witness similar condensation effects over the wings of airliners in humid air during the landing phase, when flaps are fully deployed. Here, however, the condensation does not end abruptly, since no shock is involved. Also, the disturbances produced by the aircraft do not reach out so far at lower speed, so the condensation happens only close to the aircraft's surface. Bluntness helps: The cockpit causes its own small condensation area shortly past its maximum thickness, where suction due to displacement is highest.

Just to further clarify what you touched on: once the aircraft is supersonic, the condensation cone disappears.  The cone only becomes visible during transonic flight.

Could you explain why condensation cones don't appear when travelling above Mach 1? And does a condensation cone appear when flying exactly at Mach 1?

So I understand why the vapor cone is made, but why does it appear as a symmetrical cone? Don’t certain parts of an aircraft experience more air acceleration, and therefore more vapor?

@Wyatt It is mostly caused by the displacement effect. At low level and high speed the lift coefficient in level flight is very small! For an asymmetric effect look at the rear canopy, as explained in the answer. I wish you would really read my answers!

@Konrad my guess is because other shocks might form above Mach 1 preventing the mach cone, but still not sure.

Sorry to ask another question in this comment section, but as @Konrad mentioned why does this effect not appear above Mach 1? What stops the vapor from forming when the air enters a supersonic state? (This might require a separate question, not sure)

@Wyatt It seems you missed the section that reads that air is "decelerated and recompressed by a straight shock, causing the condensation to disappear" in supersonic flow.

I recall reading that section, but I don’t know why it didn’t click (although it is late here; not thinking the sharpest). If you don’t mind one small follow up question, where exactly does the shock that causes the condensation to disappear form? For example on the wing, where along does the condensation-stopping shock form? This picture could be used as a good reference to my question. Thanks again, and sorry for missing something very obvious.

@Wyatt It is the only shockwave around: The one which ends the local supersonic area.

I see. So in the linked picture, would the shockwave you're talking about be in the 3rd figure, or the Mach 1.05 case? (the frontmost shock in the Mach 1.05 case)

@Wyatt I am growing increasingly desperate at your inability to read answers. Here it says: However, the rear boundary of the condensation is indeed caused by a shockwave. The low pressure area is instantly ended by a compression shock, when the supersonic flow around the aircraft is abruptly decelerated to subsonic speed by a compression shock.
What is more to add?
Mach 1.05 is supersonic and has no condensation cones.

I think you might’ve missed my question, as I did mix up some terminology. I am making the assumption that there is another shock that forms when you increase speed from M=0.99 -> M=1.00. If there wasn’t, this condensation would not disappear. I’m asking about that shockwave, not the one that ends the supersonic area of the condensation cone when going <M=0.99

(I can try to explain my thought process on this if that would be helpful)


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Is passenger weight distribution important on a commercial flight?
This is something I've wondered about for a long time.  On really large airplanes, like a 747-400 or A380 for example, I would assume that the weight of the passengers on board is a significant to the flight characteristics of the plane. And it seems like it would be pretty easy to put all the passengers in an odd place (like all at the front or back) and as a result significantly change the flight characteristics of an aircraft.
So, assuming I'm right (tell me if I'm not), how do commercial aircraft counter this problem? Do they do their best to distribute passengers throughout the craft with seat assignments? Or do they have ballast they can move around (like fuel ballast)?  Or is the weight shift not significant enough to warrant anything along these lines?

On the EMB-145 the passenger cabin was split into 5 zones and we were given passenger totals in each zone from the flight attendant prior to leaving the gate.  If balance is off (this happened quite rarely for us) you would tell the flight attendant "I need 2 passengers from zone 5 moved to zone 1" or "I need a passenger from zone 3 moved to zone 2" or some other similar instruction.  The flight attendant would solicit volunteers and if no one did, they would instruct someone to move.  The move was only for takeoff and once airborne they could go back to their normal seat.
After moving passengers we would re-calculate the weight and balance to verify we were in the envelope and set takeoff trim.
Similar methods are used in larger airplanes with the cabin split into zones.
The only time we would use ballast is when we had a full cabin and not enough bags in the cargo (not common).  In those cases we would ask ops for ballast and they would put something in the cargo.  They would try to make it useful if an outstation needed something else they would just load 50 lb bags of sand.

What kind of weight figures are used to determine the weights?  Do you assume everyone weighs around 150lbs?  Or is there some sensor somewhere?  I've just never been put on a scale before boarding, so I have to wonder :).

In the summer everyone weighed 170 lbs and in the winter it was 180 (or something close to these numbers).  Each airline will use standard weights which either come from the FAA (higher weights) or the airline can go through some process to use their own winter/summer weights.

So, just to check, in your experience the airline wouldn't assign seats during the ticket purchase phase in order to create a proper balance?

Considering passengers can change to empty seats at kiosks or with any agent willing to help them, I don't think there was any algorithm in the ticketing system, nor do I believe it was even aware of the passenger zones (I know it didnt know which rows had extra O2 masks, for example).  On a light flight, people also move around from assigned seats.  We check weight and balance on every departure and we are the final (and only) word in ensuring we are in the envelope.

Well, that does make sense, you are the one flying the plane after all.  Thanks for the info :).

Is the idea behind those summer/winter numbers that people actually weigh 10 more pounds in the winter, or that they have extra clothing (coats, etc.) with them?

@TimS. Extra clothing.

A few items just to add to the background info:

Large aircraft aren't just interested in being within the envelope, but also want to be close to an optimal c.g. location. For the 747-100, -200, -400 a zero fuel weight c.g. of 26.6 percent of the mean aerodynamic chord is the usual aiming point. This is done to minimize fuel burn while still staying within limits as fuel is burnt.
Large aircraft may also require different operating procedures when the c.g. is within certain parts of the c.g. envelope. The one that occurs to me offhand is the requirement for using a low-gross-weight-aft-cg takeoff procedure for 747s. There's also a restricted forward c.g. limit on the 747 when an operator has elected to use increased aft c.g. loading limits.
As your airspeed increases, a c.g. close to the forward or aft limits becomes less critical because the tail plane has more authority.

I'm not sure how sensitive/flexible the widebodies are but on the smaller regional jets, the crew will use the "whizwheel" to determine CG location.  The aircraft is divided up into n regions (depends on how large/long the aircraft is).  If the CG is too far forward, the crew will require that a few passengers to move from the forward region to the aft regions.
I'm certain that the same thing happens on the larger jets but the crews receive weight an balance from dispatch or whomever does it for them for the purposes of review.

So, to your last comment, some airlines are large enough that they calculate all of this out prior to boarding, while some airlines just do it on the ground before take off?

In those cases, the pilots will send the passenger boarding totals to dispatch via ACARS and get a report back with weight and balance information.

Jay Carr, its always done before pushback.  At some airlines, the pilots do it with the mechanical calculator "whizwheel" and paper, and some pilots get it from dispatch.  Either way, its computed and verified prior to pushback.

@h54 Sorry, I should have been more careful with my wording.  "On the ground" meant, "before pushback" in my mind.  Thanks for the clarification.

No problem at all.  Glad I could clarify.

For passenger weights, a typical airliner will use standard weights. Flights are also divided depending on short-haul and long-haul. The standard weight for a long-haul flight in my company was 81kgs. For short-haul it was 84(or 85)kgs. The rationale is that passengers tend to carry more hand-luggage on short flights and the passenger weight is meant to cater for passenger AND carry-on bags. It may seem pretty hit and miss but additional 10kgs per pax for 400pax will mean an additional 4000kgs spread throughout the cabin.. Thats a big amount but the since the aircraft weighs 350-400 metric tons it's around 1 percent. And that 4000kgs is only if everyone exceeds by 10kgs, it probably is much less as some will be over and some will be under.
Staff are supposed to look out for groups of large pax which do not fit the standard weights (think Sumo wrestling team or oompa-loompas attending a conference) and in such instances a correction is made in the load-sheet with estimates.
The short-haul weights will also change with season..factor in heavier winter clothes for that.
For distribution most check-in systems (or departure control system-DCS) have a built in logic which distributes the seats evenly unless there is intervention by the check-in agent to change the seat. In some cases the ground staff may block seats to achieve a decent trim (Balance). For example on a smaller commuter aircraft with one door for boarding (ATR 72) all passengers will want to sit in the rear of the aircraft in order to be near the door (boarding-door at rear) and be first off the plane. Since they are so much in a hurry to get off the plane they usually have only carry on bags. This means that the front of the plane has less pax and there is not much that can be loaded into the forward hold to balance the bunch of pax at the rear. In such cases the ground staff may decide to pre-seat the passengers evenly along the cabin and block other seats to ensure that a decent balance condition is met.
In flight the movement of passengers used to be managed by 'trimming' the horizontal stabilizer. With the 747-400 and MD11 the designers introduced the tail-tank where fuel was stored in the stabilizers (I think 10,000kgs for the 747-400, MD-11 less I think around 7,000kgs)
Some aircraft are a challenge to trim well, a good example is the 747 combi. With a full maindeck and light passenger load you will face problems with the aircraft exceeding the rear limits (tail too heavy) unless the guys in the warehouse loaded the really heavy freight on the lower-deck pallets which the weight n balance guy can plan for the forward hold. It got so bad that sometimes we had to upgrade pax to business class (in the nose) to achieve a legal trim..we're talking 10-20pax here, not one or two.
Not related to the original question but the catering loaded will also play an important part of the calculation. A B747-400 taking off from London to Singapore will be stuffed to the gills with food and drinks for 400 pax but for a shorter sector there will be a lot less carried.  These data are in weight-schedules the weight and balance guy will use in preparing the weight n balance document.

On an under-booked flight the passengers are spread around through seat assignments.
Emergency exits are kept clear, and if someone tries to sneak there for the extra leg room they are asked to return to their seats (at least the underage passengers are).
Source: I was on such a underbooked short haul flight for a school trip, we plus a handful of other passengers only filled a third to half of the plane. On the return flight we coincided with another school trip returning and there was a clear split between our class and the other school.

The emergency exits don't have to be kept clear. The seats next to them however may only be occupied by persons able to open them, so they have to be able-bodied and adult.


text:
What is a good plane for aerial photography?
I'm a bit of a photographer and I keep thinking it would be fun to try and do some shots aloft.  Only trick is, I'm not sure what kind of plane I would want to use to get those pictures done.  I'd have to rent the plane and the pilot and I'd like to keep the price down as best as possible...  So a purpose built plane isn't such a big deal.
Other considerations

Good view of the ground, though it doesn't have to be straight down (I'm not doing surveying
Stable while banking so I can more easily track shots when the plane is at an angle.
Ability to be held stably at a bank without actually turning the craft, again to help me track my shots.
Low vibration, for the same reason as stated over the last two.
Big windows
Can fly low and slow for if I want to get close to things (within reason.)

Also, a high wing is probably preferred.  Though, if it's exceptionally good at holding a bank, it may not matter.
If you think of anything else that I should consider to keep my camera from being jangled about, and to allow me to have a good view so I can get some shots...  Please feel free to leave them in the comments.
So, what plane would work best for this mission?

It sounds like a helicopter would actually be best for this purpose. ;)

The cost for rental would be ridiculous though...wouldn't it?  That and they tend to vibrate I thought.  Though if you want to put together the reasons why and post 'em, I'm curious.

This article on photography from helicopters might be useful, even if you do go for a fixed-wing craft.

The Abrams P-1 Explorer?

@RedGrittyBrick could you expand that into an answer with some explanation?

The Edgley Optica, it was designed for observation and photography. The right side door is clear and has a lens hole in it.

Need the plane be motorized? Gliders offer great sight at zero vibrations.

Well, the first caveat is that the best plane for aerial photography is one that someone else is flying -- Trying to set up shots while also maneuvering an aircraft is difficult at best, and can be dangerous.
Hitting your specific points:

Good view of the ground
This generally implies a high wing aircraft, assuming you're shooting from inside the plane. (If you're mounting external cameras this is much less of a consideration.)
Stable while banking & Able to fly banked without turning
Properly flown pretty much any aircraft can fly along indefinitely in an aerodynamic slip -- it's not an aerodynamically favorable configuration, but meeting this requirement shouldn't be a problem.
The need to maintain the aircraft in a slip is however one of the reasons you probably want to have someone else flying. While not difficult it is not the way the plane "wants" to be flying.
Low Vibration
Give up the idea of long telephoto lenses or slow shutter speeds -- at least unless you have some kind of image stabilization in your lens/camera.  Most GA aircraft will have some appreciable vibration.
Big Windows
"Big" may be less important than "Removable" -- Most light GA airplanes will have windows of a reasonable size (at least in the front seats), but aircraft plexiglass windows are not of the best optical quality, so you might not want to shoot through them.
Able to flow low and slow
The optimal aircraft here is a helicopter (in fact some might argue that the R22 helicopter is a great photo platform - but beware the vibration), but most GA training airplanes can do an adequate job here.
Again, a plug for having someone else fly: Trying to photograph something on the ground while flying low and slow is a recipe for a "moose stall", which frequently doesn't end well for anyone except the moose.

My recommendations
In the typical GA airplane fleet I would pick a Cessna 152 or Cessna 172. These planes are pretty much ubiquitous, and among their advantages are the large hinged windows which you can flip up and pop a camera out of.
You might also consider "jump planes" which are certificated for flight with a door open or removed, providing you a giant hole in the fuselage through which you can take photos (as well as anchor points to attach yourself and your equipment to the airframe).
If you will need to hold station over your target a R22 or similar helicopter would probably be your best choice (and the R22 can certainly be flown without doors).
Protecting your equipment
At a bare minimum you should be wearing a substantial wrist strap. Anchoring yourself and your equipment to the airframe is also an excellent idea, as having expensive camera gear fall out of an aircraft can be quite unpleasant (both for you - as the gear will likely be destroyed - and for people on the ground who get clobbered by it).

For the record, I did mention in the original question that I would be hiring a pilot to fly me.  Just sayin'.  Also, regarding vibration, don't some props cause less vibration than others?  I thought tri and quad blades weren't so bad?

@JayCarr If you handhold, vibration won't be the issue - your body is an excellent isolator at engine vibration frequencies. Turbulence will be a problem though, and if you brace the camera against the airplane in any way the vibration will be intolerable in any plane. Check out Kenyon gyro stabilizers for turbulence if your budget allows. They can be bought for about $1,000 or rented cheaper. And use a plane you can open the windows in or the glare and scratches in the acrylic will ruin the shot. C152/172 both have semi openable windows.

In most GA planes (and presumably helicopters though I don't know much about those) there are power settings that induce more or less vibration - you'll be able to feel any vibration that will affect your shot, and can usually adjust power accordingly. Like @dvnrrs said though, the body is a great shock isolator. Mounting to the plane is where you may need special equipment.

@voretaq7 Mkay, I'll keep that in mind.  Probably would be a good thing to chat with the pilot about before heading up... Just wish I could combine this answer with Pauls, he got the "which pilot to hire" about perfect.  But, I prefer this one because it covers the plane aspect of the questions better...

@voretaq7: would you say that you've changed your mind over this, or is there a difference in how this question is worded that makes this question appropriate?

@Qantas94Heavy Yes and No - to me this is a question that can be "answered" (at least to some degree) with factual information (characteristics to look for in a photo plane). That's as opposed to the sort of "recommend a plane for this mission" stuff I was thinking about in that Meta answer ("I've got a husband, two kids, and a dog, and we go to Grandma's 500 miles away every month -- what kind of plane should I buy?") which has a lot more subjectivity

I used to work at a sport parachuting center - we occasionally had photographers rent one of our Cessna 182 airplanes for the same purpose. An advantage of jump planes is the pilots are quite used to odd attitudes (and even odder requests) so a 60 degree bank angle with the door open and you leaning out of it will get a reply of "no problem".
Our conditions were the photographer wears a parachute, a seatbelt, and if the camera goes for a jump that's just too bad for your wallet. 30 minute lecture on what to do if you fall out. Short form: drop camera, grab this handle, pull. And the trip's over if you do anything silly.
You would sit on the floor where the co-pilot's seat would normally be, the pilot will open the door as needed, and you have a clear view out the right rear quarter of the plane. Obstacles are the wheel (front half of the door looking down) and wing strut (forward) - the tail is well out of the way. It's very noisy, but unless your camera is actually outside the fuselage the wind blast is not an issue. Don't change lenses though, and your clip-on lens hood will probably disappear rather quickly.
You can sit on the door ledge with your feet outside and have an excellent, stable field of view with both hands free to operate your camera. I've sat there hundreds of times without a seatbelt, it's no problem even in steep turns. Just a bit odd seeing the ground above the wingtip. Difference is, I don't care if I fall out.

Excellent answer paul, I hadn't really considered using a jump company, but when you put it in that context it makes a lot of sense.

I mean, having a pilot who is used to having passengers hanging halfway out the door would be optimal, I would think.  We have a company that does jumps here, I wonder if they also have a 182 to rent out...

A 182 is basically the standard jump plane, unless the place is busy and has all-turbine aircraft. A quick check of dropzones near Springfield doesn't list their aircraft on websites but they will either have one or know who does have one - it's a rather small community.

Sweet, I'll check that out then, thanks :)

Chris Dahle-Bredine (author of Shot From Above) uses an ultralight for this kind of photography.
It's cheap, only burns a little gas, is cheap to maintain, has lots of visibility, and he takes amazing shots!

Ultralights are perhaps the one exception to "the pilot shouldn't be the cameraman" - and the visibility out of a powered parachute certainly can't be beat!

Yes, ultralight is also the way to go: I know of a Humbert Tétras used for a large scale aerial survey here in Madagascar.

I'm going to try to offer an out-of-the-box solution and suggest a remote-controlled quadcopter / octocopter UAV with a camera mounted on it.  Such a system seems to satisfy most of your stated and implied needs:

I'd have to rent the plane and the pilot and I'd like to keep the price down as best as possible.

A UAV seems like an excellent choice in this regard: unmanned vehicles tend to be cheaper than manned ones, and don't require a pilot's license to operate (although other regulations may still apply).
You probably do still need a skilled operator, since controlling a quadcopter does take some practice, and it's difficult (not to mention potentially dangerous) to control the vehicle and the camera at the same time.  Having a separate pilot frees you from having to do that job yourself, and lets you concentrate fully on taking pictures.  The commercial operators I know of that do this kind of work always have a separate pilot and camera operator.

Good view of the ground, though it doesn't have to be straight down (I'm not doing surveying). [...] Big windows. [...] Also, a high wing is probably preferred. Though, if it's exceptionally good at holding a bank, it may not matter.

Check.  The setups I've seen usually have the camera mounted under the vehicle body, so you can point it in any direction, including straight down, and the only things that could possibly get in the way are the landing struts.

Stable while banking so I can more easily track shots when the plane is at an angle.
Ability to be held stably at a bank without actually turning the craft, again to help me track my shots.

Check, sort of.  No, the quadcopter itself can't maintain a steady tilt without accelerating, but the rigs I've seen let the camera be held steady at any angle, while the copter can freely move in any direction in three dimensions.

Low vibration, for the same reason as stated over the last two.

Check.  At least, I've never heard of this being a problem.

Can fly low and slow for if I want to get close to things (within reason.)

This is the one aspect in which remote-controlled helicopters absolutely excel: they can hover in place, or move at any desired speed (for panning shots), at any altitude above ground level.  Want to hover in front of someone's face to shoot a portrait of them?  Perfectly possible (if maybe a little bit unnerving).
Mind you, I haven't actually flown or worked with such systems myself; most of my knowledge comes from watching a demonstration at a "maker faire"-style event by a local company operating such systems, and exchanging a few words with the folks there.  But it was definitely impressive, and the way I would go if I ever needed to do some aerial photography.
That said, there certainly are also some photography applications for which remote-controlled vehicles are not so well suited, such as high altitudes, very long flight times, flight over significant distances of inaccessible terrain or operation in bad weather.  However, if your requirements don't include any of those, they may well be much more practical and less costly than renting a manned aircraft.

Ah, see, but you missed the more important implied criteria: I like making up reasons to fly in an airplane ;).  But yes, other than that, a quadcopter sounds like a pretty good idea.

I was going to post a similar thread.   As much as a hate the UAV/drones for most low level aerial photography of the ground they seem to be a great tool.  in fact I am going to be getting at quad or hex-copter this fall to play with  aerial photography.    Maybe I will get this video of a rocket. https://www.youtube.com/watch?v=9ZDkItO-0a4

Well, the absolute cheapest and easiest way for aerial video is with a homemade garbage bag kite. Don't laugh, sometimes you can get great results. And you can easily change the viewpoint angle by simply reeling the kite in, adjusting the camera to a different view angle, and reeling it back out. You can also fly all day as long as you got wind.  Here's how.
http://quadcopter101.blogspot.com/2014/04/do-you-wish-to-do-aerial-video-but-only.html
But another cheap and easy way is with a toy quadcopter.  And again you can get surprisingly good results with even the cheapest (about $65) quadcopters.  Again, here's how:
http://quadcopter101.blogspot.com/2014/02/misc-4-aerial-video-part-2.html

I have done kite photography.  Expect to spend at least $100 on a "lifter" kite and Picavet mount.

How about the AirCam?  It was pretty much designed for the type of aerial photography you describe - low and slow with great visibility.


text:
What exactly is a QRH?
In this question about aircraft dumping fuel I was told that there may possible be guidance in the QRH.  I know that there are a lot of guidelines given to pilots, but I've never heard of this one.  Would anyone care to explain, from a pilots perspective, what exactly a QRH is and how it's used in modern aircraft operation?

See how it looks like here. This is a B737NG QRH.

A QRH is a Quick Reference Handbook and is an approved (by some overseeing entity) document specific to an airplane and operator that contains checklists for just about anything the airplane can experience.  At my airline we had copies in the airplane and also in our company flight manual (CFM).
The entry point into a QRH checklist is one of a few things

Memory items
EICAS message
An abnormal event

For option 1, there are various checklists that must be memorized and performed at a moments notice with no reference to the checklist.  Some of these are things like trim runaways, engine fire/severe damage, emergency descent.  Once the memory part of the checklist is complete you refer to the printed version of the checklist in the QRH to verify and perform additional steps beyond the part you were required to memorize.
For the other options, any time anything abnormal happens or an EICAS message is presented, there are indices by procedure name and also by EICAS message into a specific procedure in the QRH to follow.  These procedures may reference other procedures.
For example, If I were to experience a dual engine failure, I would pick up my QRH and find the procedure "DUAL ENGINE FAILURE", this procedure says I should have the master warning light illuminated (and an aural triple chime) and I should see the EICAS message (in red) "ENG 1-2 OUT".  After verifying this presentation and verifying I am in the right procedure, I would perform:
Airspeed....................MINIMUM 260 KIAS
Altitude....................MAXIMUM FL250
Oxygen Mask (if required)...DON
APU.........................START
ENGINE AIRSTART procedure...PERFORM  (note, this is another QRH procedure)

CAUTION: IF THE APU HAS BEEN USED TO START THE ENGINES,
         DO NOT ALTERNATE THE FADECs AFTER START

Note: If the APU is not available, only equipment supplied by the
      Essential DC Bus 1 and 2 will be available.  Engine windmilling
      should drive engine driven hydraulic pumps and supply hydraulic
      pressure.

IF neither engine can be restarted:
    DITCHING or FORCED LANDING procedure......PERFORM

It does not have to be FAA approved. It has to be approved by appropriate overseeing authority (I am not sure whether that is country of operator, country of registration or country of manufacture though).

@JanHudec thanks for the clarification.  I have edited the answer to reflect your comment.

A QRH is a Quick Reference Handbook.
It is basically the checklist used in the aircraft along with other useful information, which varies from QRH to QRH, but can include things like system diagrams, maximum cruising altitudes for the current conditions, takeoff and landing performance, etc.
It is usually a small form, spiral bound document that is convenient and easy-to-use in the cockpit:

Among the important features of a paper QRH are the tabs, which make it "quick" to find the section you need. (You can sort-of see them above, this example has nice big ones)

@voretaq7 Ahh yes, that would be the "quick" portion of QRH!

Airlines that operate aircraft originally built for other airlines also put in the QRH the differences between the various airplanes. The more different aircraft of the same model the airline operates, the thicker the QRH becomes. Unfortunately the thicker it becomes the less quick it becomes. Both 747 carriers I worked for had aircraft from five or more carriers that had originally ordered the airplanes. Former TWA airplanes were the most different, especially the pilots forward overhead panel.


text:
How do aircraft windshields not crack when flying at supersonic speeds through precipitation?
Randall Munroe (author of XKCD and What If), once wrote a What If about how fast one would have to drive a car in order to have rain water shatter the windshield.
In the post he mentions that water hitting a windshield at supersonic speeds has the potential to shatter the glass.**
The article, unfortunately, is only talking about automobile glass.  And while I'm sure it's true that automobile glass would shatter if rain hit it at super sonic speeds, it's pretty clear to me that the glass on supersonic aircraft is not shattering when it flies through precipitation.
So, what is done to a super sonic aircraft's windshield to keep it from shattering when flying through precipitation?

** Here's a block quote of all the pertinent text in the post from Munroe.  I figured I'd post it for those who are Too Lazy™ to go read the article.  (Though, honestly, you ought to.  It's informative and entertaining.)

Here's what happens when a raindrop hits a glass surface at high speed:
  When the droplet makes contact with the surface, a shockwave travels back up through the droplet...
...Normally, this shockwave would move at the speed of sound within the liquid—about 1300 m/s, four times faster than in air. However, at high impact speeds, this shockwave actually moves substantially faster than the speed of sound in water.
The water is squeezed between the incoming drop and the glass surface, which makes it squirt sideways in all directions. These jets of water can move even faster than the original (already supersonic) droplet, and even faster than the shockwaves we mentioned...
...The sharp pulse from the shockwave can crack glass...
...In addition to the direct downward pressure, the water jetting sideways can cause damage, too. If the material has any microscopic holes, cracks, or bumps, those jets can strike them and create new cracks or widen existing ones.
source: What If #93, Randall Munroe

It does not say it could crack the glass, just that it will erode it.

@JanHudec The implication is that eventually the weakening of the glass would cause a car window to crack.  If it cracks enough it would eventually shatter because of the pressure being exerted on the windshield, right?

@JanHudec Though I did change the title question to read "crack" so that I'm not taking logical leaps from the text I included from the original post.

Aircraft don't go supersonic in rain/icing conditions/hail.

... it's stronger glass ... why would planes use the same type of windshield as cars?

Interesting information: SR-71 Blackbird's "windshield" would reach 600 degrees Celsius during hypersonic flight.

Sometimes a question comes along that you never think about because it's "obvious" but which leads to very interesting answers -- good work.

@Simon: ...and if the rain wasn't expected?

The Concorde had 2 discrete windshields for different stages of flight. During subsonic flight (mainly take off and landing) the nose was drooped and the inner windshield was exposed. For supersonic flight the Concorde would raise its drop nose which also contained an outer windshield that would cover the inner windows. This outer windshield was made of special heat resistant glass that was also tinted. It can be assumed that this outer windshield could also withstand any pressure exerted during supersonic flight. The bigger problem in the Concorde was heat: the nose had to have fuel pumped through it just to keep it cool enough. For what it's worth the Concorde flew at about 50,000ft when it was supersonic; this is well above most weather systems.
Drooped

(source)
In Place

(source)
If you are interested, there is an old paper you can find here that covers windshield failures and lists the Concorde as the #2 aircraft for it (747 comes in at #1) over the years the paper covers. Interestingly enough here is a table of causes:

Heat fatigue and manufacturing defects (what I assume they mean by saying the windshield itself is the issue) are the primary cause of the issue according to this data. Here is one of the patents filed for what appears to be the Concorde windshield; it's an interesting read!
Going further, if we look at the most extreme case of supersonic planes, the SR-71 Blackbird, the inside of the windshield was in excess of 120°C and the exterior of the nose area would be closer to 260°C during supersonic flight. This would turn any water into vapor if it came into contact with the surface. While I don't know the specifics of that, the Blackbird flew at close to 80,000ft, so it too was above most (if not all) weather. I can't yet find an official quote of what that windshield was made of, but heat was still a larger issue than hitting rain.

(source)
Here is an interesting paper on what happens to water droplets when they suddenly encounter a high-speed airstream. It might suggest that such an impact with an aircraft would also cause vaporization, aside from the heat of the surface causing it.
Even subsonic aircraft windshields are extremely strong; they can take continuous hits from solid hail chunks and not shatter.

(source)

That hail damage picture is intense.  I wonder how the nose can look that bad but the engines and nacelles seem to be relatively unharmed? (not really expecting an answer)  Thanks for the picture and link!

Looks like Randall Munroe (whom I admire greatly) might have missed a chance to write that the car windshield in question (and the rest of the car) would heat up and suffer other damage before rain would be a factor - although he did point out that the car as a whole would encounter a lot of trouble even reaching such a speed.

80,000 ft is well into the stratosphere and there are no clouds there, ever. Even normal flight levels ~32,000–42,000 ft are above most clouds (average altitude of tropopause is 36,000 ft).

Note that it's "Concorde", not "the Concorde".

@JPhi1618 The nose houses the weather radar and therefore needs to be made of a material transparent to radar. That means no metal. The engines and their nacelles are a bit more sturdy than that.

In fact, if that diagram is accurate, the SR-71's canopy was the hottest non-engine part of the plane.

Okay, now I'm wanting to know more about the aircraft whose windshields were broken by "Lightning Damage" and "Crew Procedures"...

That 737's windshield did shatter; it just didn't come apart.

The first trick to make windshields stronger is used also in aerodynamics: Sweep reduces the effects of speed. Giving the windshield an inclination both back- and sideways will reduce the impact energy of whatever hits it in flight direction.

X-15 carried by a B-52 (picture source). Note the angled windows: They were oriented at 75° to the air stream, so an object hitting them at 2,000 m/s (Mach 6.65 at altitude) would "feel" like an impact at 500 m/s against a surface at right angle. Not that it would rain at 80 km up, so this was mostly for aerodynamics.
And the second trick is used always if things are at the risk of breaking: Make them thicker! The thickness of a supersonic fighter canopy is approximately 20 mm and that of an airliner even 50 mm, whereas your average car glass is only 4 to 6 mm thick. Also, windshields are multi-layered: In airliners as in cars, they are made from tempered glass and polyvinyl butyrate, and the spherical canopies of fighter jets made from polycarbonate, polyurethane and acrylic.
Finally, the goal of the engineers is only to make the structure withstand the impacts over a certain time, which can be only minutes for supersonic flight. Birdstrikes are one-time events, but rain impact is an ongoing process which erodes any surface over time. The single raindrop or hail impact will only cause local, microscopic damage, but enough of them over time will wear down any structure.

50mm?! That sounds like it would cause some non-negligible refraction.

@shortstheory: That is why they are flat. Curved windows are thinner and sometimes even need grinding to get their optical quality right.

How do aircraft windshields not crack when flying through precipitation at supersonic speeds?
You are talking about a phenomenon called rain erosion at supersonic speeds.
See: INVESTIGATION OF THE PHENOMENA OF RAIN EROSION AT SUBSONIC AND SUPERSONIC SPEEDS
Just because a small steel ball of mass m, traveling at supersonic speeds, can crack a windshield, it does not mean a water droplet of the same mass and velocity will produce the same effect even if it has the same energy.
A simple explanation can be given based on elastic and inelastic collisions theory, you know from school. The steel ball hitting the glass is in the elastic collision case characterized by high interaction forces, at least up to the moment the glass breaks. The water drop is in the inelastic situation, the impact forces being lower.
We are in the case of a soft ball and a stone of the same mass hitting a window with the same speed. In the first case the glass survives in the second breaks.

Not sure where you attended secondary school, but elastic and inelastic collision theory certainly was not covered in my high school! Since I didn't study physics or math in college, I didn't learn much about it there, either. :(

About inelastic collisions you can read here: https://en.wikipedia.org/wiki/Inelastic_collision . The main idea is that the kinetic energy of the droplet relative to the plane converts in heat quickly in a fraction of a millisecond as the droplet smashes against the window.and so the water drop loses its high speed.

Highschool elastic and inelastic collision theory is generally useful, but ignores supersonic shockwaves. Note that supersonic in this context refers to the speed of sound in the colliding materials (glass/water), not the sound of speed in air. The former is several times higher.

In my case (further maths A level in the UK), elastic and inelastic collisions were covered in high school as far as conservation of momentum and energy, but not not to the detail level of shockwaves and interaction forces.

@FreeMan Where I was it elastic and inelastic collisions were just part of the Grade 12 physics course.

Because aircraft don't regularly fly at such speeds at altitudes where this might be a concern.
The quoted problem (hitting a drop of water faster then the speed of sound in water) is never faced by any real aircraft. Even if because of the shock-wave there was no windshield in existence that would survive that impact, it wouldn't pose a problem, because no aircraft flies at Mach 4 at an altitude where it can encounter rain.
Actually, no aircraft was ever capable of cruising at Mach 4. Besides some experimental prototypes, no aircraft could even fly at Mach 4.
Even the handful of aircraft which can reach about Mach 3, can only do it high in the stratosphere, where the air is much thinner and there is no rain.
Therefore, hitting a raindrop at Mach 4 is not an issue, because no aircraft can fly that fast. Actually, no aircraft flies much faster than Mach 1 at altitudes where rain is possible.
Even the planned future aircraft which will be capable of sustained flight over Mach 4, will fly at that speed only when high above the clouds, because they would not be able to fly that fast where the air is thicker.
EDIT:
Even if the problems would arise at Mach 1, aircraft regularly fly supersonic only in the stratosphere, where there is no rain. Actually, very few aircraft fly supersonic: airliners (except for the Concorde) are all subsonic, and even the Concorde only flew supersonic when it was flying high enough. Military aircraft, although many of them capable of supersonic flight, rarely ever fly supersonic, and even then only for short bursts.
So, summarized:

supersonic aircraft fly usually not much above the speed of sound and so they can easily slow down to subsonic speeds when encountering rain. (maybe someone can help out whether there was anything in the Concorde flight manual about the maximum allowed speed in rain)
aircraft rarely (if ever) fly supersonic at altitudes where rain is a concern.

The question is saying that the craft is flying at supersonic speeds for air, I should probably go back and clarify that...

Yes, but the problem Randall Monroe mentions only arises when flying at the supersonic speed for water.

I think you ought to read the full article.  But, to clarify, he is saying that when you collide with water at mach 1, the pressure wave travels through the water droplet at 4 times the speed of sound (in water).  Which is much faster than energy normally travels trough water.

@JayCarr, the article is ambiguous, as is saying Mach 1 and speed of sound, because they can all mean either in air or in water. The article does, however, at one place mention 500 m/s, which is ~M1.47 at sea level and ~M1.67 at 36,000 ft in air in ISA (sound is slower when it is colder).

@JayCarr: As I understood it, the droplet hits the glass at a speed which is supersonic in air but subsonic in water. Therefore, the pressure wave can travel into the droplet, which happens at the speed of sound in water. This pressure change now will squirt water sideways, and this happens at water's supersonic speed. It is this sideways squirted water which causes most erosion.

@PeterKämpf Monroe stated that, for some really weird reason, the pressure wave actually goes faster than the speed of sound in water (which doesn't make sense logically, I admit.)  But he may be wrong, he is a rocket scientist after all, not a fluid dynamics expert.

@JayCarr: Monroe says that normally the shock wave travels at the speed of sound. Only if the orthogonal component of the impact speed is higher than that (meaning a flight speed of >5800 m/s in case of the X-15 windows) would the shock wave travel supersonically. This is all correct and not weird at all.

Also bear in mind that when a droplet of water approaches a supersonic airplane windshield, it first encounters a supersonic skin layer of air, which would tend to buffer and deflect some component of the force before it hit the windshield itself.  That is not to say that objects are prevented from hitting the glass...they do it all the time...but rather to say that much of the force will be dissipated, diminishing the urgency of the problem.

Not just that; in all (?) supersonic aircraft the windshield and the whole cockpit is behind the nose cone of the aircraft itself. The nose creates the first shockwave, and the stream behind it is already slower and hotter and has higher pressure. This alone may be enough to evaporate droplets, though I don't know for sure.


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What are the pros and cons of single-engine vs. twin-engine?
Why would someone prefer to own a single-engine vs. a twin-engine airplane?
What are the pros and cons of each?

This old AvWeb article might be of interest.

No-one going to do the old saw about when the first engine fails on a twin, the second will get you to the site of the accident?  Me neither!

hahaha (9 more to go....)

That may be true for Part 23 aircraft, performance on 1 engine does not need to meet the much stricter requirements that Part 25 imposes.

I own a twin and a single. A single is far safer as shown by every NTSB study done since the 1960’s.

In the light aircraft world there are a few trade-offs to consider.  The short version:
Single-Engine Pros:

Simplicity
One engine means fewer controls, a simpler fuel system, simpler vacuum system, simpler electrical system, etc.
Operational cost
Only one engine to feed, so you spend less on - fuel & oil per flight.
Maintenance cost
Only one engine to maintain - One set of spark plugs & cylinders, One engine to overhaul.

Single-Engine Cons:

No redundancy: You have one engine, if it fails you're a glider.
Singles generally tend to have less spacious cabins than twins.

Twin-Engine pros:

Redundancy
If you lose an engine the other will give you a chance to get to a landing site.
Cabin space
If you step up beyond "twin trainers" you can get a very nice cabin in a piston twin.
Equipment
Again, if you step up beyond the "twin trainers" twin-engine planes tend to be "traveling aircraft", so they often come with nice features like deice/anti-ice equipment.

Twin-Engine cons:

Operating costs
Two engines to feed (fuel & oil costs double).
Maintenance costs
Two engines mean twice the cylinders, twice the spark plugs, etc.
Complexity
The redundancy you can get in a twin comes at a price: Synchronizing the propellers, a more complex fuel system (crossfeed), paralleling alternators, vacuum system failover, etc.
Short and Soft field performance can be lacking.
Failure of an engine can be problematic.

In addition to the operational considerations there are some other practical items to consider: twin-engine aircraft require a multi-engine rating (which means more training time). Twins will also generally be more expensive to purchase/rent (and may be more difficult to rent when away from home), and will likely cost more to insure (particularly for low-time pilots).

This may sound naive, but is there no power / speed difference?

@WalrustheCat There is absolutely a power difference, and usually a speed difference, but it might not be what you expect: the Seminole is a twin with 360HP that cruises at 162kts with a full-fuel payload of 543lbs, the Arrow is a 200HP single and cruises at 137kts with a full-fuel payload of 528lbs, and a Cirrus SR20 (also a 200HP single) will do 155kts with a full-fuel payload of around 550lbs.

@WalrustheCat Continuing from the example in my other comment, if you expand the list of singles to include  High-Performance aircraft you can find planes like the SR22 (310HP - 50 shy of the Seminole's combined horsepower) which will leave a Seminole in the dust in terms of both speed and useful load, and do so while burning less fuel.

My granddad always said multi-engine aircraft were difficult to trim...that's not mentioned in this answer though. Is his opinion valid or..?

The training element is underplayed here, and is the leading cause of single engine out fatalities in GA twins.

For a lot of people, the extra cabin space of a twin is not a plus.  It's like why I choose to drive a Miata rather than a Suburban.  Likewise with speed &c: I can probably operate the low-powered single out of a lot of strips that couldn't handle a high-performance twin.

@elrobis In my experience multi-engine aircraft as a class are no more difficult to trim in the pitch axis than single engine aircraft as a class as long as both engines of the twin are operating. Of course, if you've lost an engine on a twin, trimming then becomes more of a problem in all three axes. Is it possible your granddad was referring to the need to keep the rpm of the engines in synch? That is difficult to do on older twins that do not have automatic propeller synchronization.

Terry, that's possible. He was flying in the 70's so I'm not sure how that factors in. Unfortunately it's not a conversation I personally had with him, but something my mom recalled him saying. It's also possible he was referring to an engine-out scenario like you alluded to.

Don’t forget that singles are proven safer. Every study done by the NTSB since the 60’s shows that an engine failure in a twin is more likely to be fatal than in a single. A twin with one engine out is a handful. I have a Mooney and an Aztec.

Insofar as the safety issue that's been mentioned in the previous answers, there's a historical perspective on the question. Engines are far more reliable than they used to be, and turbine engines are typically more reliable than piston engines.
As I remember, most pilots coming out of WW2 (including my father), considered twins safer than singles, certainly for over-water operations, but with the caveat that the pilot of a twin losing an engine had best be proficient in handling that.
Engine technology changed. For example, the Cessna AT-17/T-50/UC-78 Bobcat, with two radial engines, was a 5-place twin in use through and after the war. Certainly an argument could have been made that it was safer than single-engine planes with radial engines in use just after the war. I certainly felt that way, an opinion gotten from my father. However, by the time the six-seat Cessna 210 came along with it's horizontally opposed engine and flying higher and faster than that old twin, my guess is that most pilots familiar with both aircraft would prefer the single. I certainly did, especially since I saw two engine fires that happened when starting the T-50 radial engines.
Now bring on the turbine-powered singles. My guess is that most pilots would prefer a single turbine-powered aircraft to a horizontally opposed twin. Having spent a lot of time in twin-engined, horizontally opposed, Cessna 310s (including one engine failure), personally I would opt for a single turbine, especially if it was a PT6 or Garret TPE331.

I dig your reflecting on the experience and opinion of the WWII flyers in this respect. This is wildly naive I'm sure, but I always romanticized the idea of bringing home a crippled, shot up B17 and landing it against the odds amidst the other-worldly flight characteristics of odd engine configurations, weird drag, and non-functioning control surfaces. But I recently read A Higher Call and got a reality check. The idea of saving the day is compelling, but there were alot of other forces to contend with, especially early in '43 when the Luftwaffe was at the top of their game.

There are single engine, long range, large cabin aircraft. A  Flying Magazine article takes the example of the PC-12 in discussing single engine benefits:

All of the size, range and payload capabilities of the PC-12 flow from the fundamental design choice of using only one engine. Carrying the fuel to feed a second engine, plus the weight and drag of the engine itself, all cut into range and payload. The second engine and its costs also mean the twin-engine turboprop that comes closest to the PC-12 in cabin size and full fuel range falls hundreds of miles short when the same payload is aboard, and costs at least a million dollars more to buy.

The con of having just the single engine is of course the consequence of an engine fail. If the single engine is very reliable this may be considered a moot point, especially since:

Single engine aircraft are certified under CFR 14 Part 23: it may not have the ability to climb and the operational redundancy after engine fail that Part 25 aircraft must have. So having a twin engine Part 23 aircraft may make the owner feel good about redundancy, but the aircraft's certification rules never demanded this to be demonstrated.
A twin engine has twice the chance of engine failure that the single engine has!

An aircraft with a very reliable single engine therefore seems to be the best choice under Part 23.


text:
Is there a system where plane/heli auto adjusts prop pitch/mixture?
This one is simple: is there a system that automatically adjusts things such as:

Mixture (I Am bored of listening for engine sounds)
Prop Pitch (I Hate auto adjusting "gears")

So I can only spend time adjusting throttle ?

Some aircraft do this, like the diamond DA40, but I don't know of any helicopter that does.

Piston engines can be equipped with ACFPs (altitude compensating fuel pumps) that autolean if they are rigged correctly.  the A36's IO-550 has an ACFP, for example.

There sure is but it is generally independent of what is traditionally considered a "glass cockpit" and is often wrapped up under the FADEC system. One of the earlier production designs for this found its way into the Mooney M20PFM which was a Porsche Powered Mooney that had an electronically inject 3.2L Porsche car motor in it. Most importantly it had "single lever operation" where the throttle, prop, and mixture were all wrapped into one lever. For a variety of reasons the plane was ultimately a failure and I do not belive any are still flying with the Porsche motor.
As Ron mentions in the comments some of the Diamond's like the DA42 are set up this way.

So I can only spend time adjusting throttle?

This is perhaps the more important part of the question. Perhaps one of the main reasons that planes are set up with the throttle, prop and mixture adjusts is to allow for fine control. Automatic control systems generally operate in the most "efficient" range but as a pilot you may wish to operate in other ranges, run lean of peak or cruise at a very slow but efficient burn. Your POH will give you all the relevant information to operate your plane in all sorts of ways.

The Diamond demonstrates that the single thrust lever is all you really need. Are you sure all those adjusting levers are not just a leftover from the olden days?

The BMW 801 had such a thing, essentially a mechanical/hydraulic analog computer which allowed to automatically adjust prop pitch, mixture, supercharger settings and ignition timing, all with a single lever in the cockpit.
It was designed by Heinrich Leibach and so complex that it was said only a handful of experts truly understood how it worked. It was called Kommandogerät and Wikipedia writes it

could be considered to be a precursor to the engine control units used
  for many vehicles' internal combustion engines of the late 20th and
  early 21st centuries.

BMW Kommandogerät (picture source)
Internal workings of the Kommandogerät (source):

This should illustrate that it was indeed possible since 1940 to allow single-lever control of an aero engine, but doing so before electronic computers became cheap and reliable enough involved a very complex device. All other engine designers concluded that separate levers for prop pitch and mixture would be better, pilot workload be damned.
The almost non-existent technological progress in aero piston engines in the last 60 years means that only spillover developments from the car industry would introduce electronic engine control systems into aviation use, such as the PFM 3200 in the 1980s and Thielert (now Continental) Diesel engines more recently.

And Austro engines, in the DA42, basically a Mercedes diesel engine adapted for aeronautical use. We had a demo in one at the factory in Wiener Neustadt, the pilot made a point of demonstrating that all he had to do to start the engine was to push a button, all he had to do to increase throttle was to push one lever only. Demo-ed flying on one engine, also a non-event. Brilliant. It uses jet fuel as well.

Our company, Flight Enhancements, has an STC for a semi-automatic, add on mixture control device called Auto-Lean. It is STCd for many single engine general aviation aircraft.  It allows the pilot to select their preferred mixture setting for phase of flight and flight profile (ie. climb, best power, efficiency, descent, LOP, ROP) while doing the actual setting automatically.  It can also hold the setting and warn of any problems.  See www.flightenhancements.com for details.